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django-athumb 2.0

A simple, S3-backed thumbnailer field.

# django-athumb

Storing images and their thumbnails on S3 is a bit of a clumbsy endeavor with
Django. While this Django app may work with more typical storage backends, it
is intended to accept image uploads, thumbnail them, and upload the original
plus the thumbs to S3. You may then get to the thumbnails in your template
by doing something like:

    <img src="{% thumbnail some_obj.image '80x80' %}" />

This automatically assembles the remote S3 URL to retrieve the thumbnail from.
No error checking is done, and several assumptions are made for the sake of
speed.

## Advantages of django-athumb

The primary advantage of django-athumb is that, unlike sorl and others,
thumbnails are generated at the time of user uploading the original image.
Instead of generating thumbs on-demand and making the user wait, we get that
out of the way from the beginning. This leads to a few big benefits:

* We never check for the existence of a file, after the first save/upload. We
  assume it exists, and skip a whole lot of Disk I/O trying to determine that.
  This was horrendously slow on sorl + S3, as it had to hit a remote service
  every time it wanted to know if a thumbnail needed generating.
* Since we define every possible thumbnail in advance via models.py, we have
  a defined set of possible values. They can also be more intelligently named
  than other packages. It is also possible to later add more sizes/thumbs.
* This may be ran on your own hardware with decent speed. Running it on EC2
  makes it just that much faster.

All code is under a BSD-style license, see LICENSE for details.

Source: http://github.com/duointeractive/django-athumb

## Requirements

- python >= 2.5
- django >= 1.0
- boto
- PIL

## Installation

To install run

    python setup.py install

which will install the application into python's site-packages directory.

## Configuration

### settings.py

Add to INSTALLED_APPS:

        'athumb'

Add to TEMPLATE_CONTEXT_PROCESSORS in settings.py:

    'django.core.context_processors.request'

If you want S3 storage as your default file back-end:

    # If you don't want this to be the global default, just make sure you
    # specify the S3BotoStorage_AllPublic backend on a per-field basis.
    DEFAULT_FILE_STORAGE = 'athumb.backends.s3boto.S3BotoStorage_AllPublic'

Then setup some values used by the backend:

    AWS_ACCESS_KEY_ID = 'YourS3AccessKeyHere'
    AWS_SECRET_ACCESS_KEY = 'YourS3SecretAccessKeyHere'
    AWS_STORAGE_BUCKET_NAME = 'OneOfYourBuckets'

## Using in models

After you have all of the above configured, you're ready to start using
athumb in your models. Here is an example model with a thumbnailing field.

    from django.db import models
    from athumb.fields import ImageWithThumbsField
    from athumb.backends.s3boto import S3BotoStorage_AllPublic

    # It is generally good to keep these stored in their own module, to allow
    # for other models.py modules to import the values. This assumes that more
    # than one model stores stuff in the same bucket.
    PUBLIC_MEDIA_BUCKET = S3BotoStorage_AllPublic(bucket='public-media')

    class YourModel(models.Model)
        image = ImageWithThumbsField(
            upload_to="store/product_images",
            thumbs=(
                ('50x50_cropped', {'size': (50, 50), 'crop': True}),
                ('60x60', {'size': (60, 60)}),
                ('80x1000', {'size': (80, 1000)}),
                ('front_page', {'size': (120, 1000)}),
                ('medium', {'size': (161, 1000)}),
                ('large', {'size': (200, 1000)}),
            ),
            blank=True, null=True,
            storage=PUBLIC_MEDIA_BUCKET)

A few things to note:

* The tuples in `thumbs` are in the format of `(name, options)`. The value
  for `name` can be whatever string you'd like. Notice that you can make the
  names dimensions, or something entirely different.
* The `storage` keyword is important, used for specifying the bucket for the
  field. If you don't specify `storage`, the default backend is used. As a
  shortcut, you could set `S3BotoStorage_AllPublic` as your default backend,
  and the `AWS_*` values would determine the default bucket.

### Backends

django-athumb comes with a simplified s3boto backend, modified from those found
in the django-storages project. For most cases, you'll want to use
athumb.backends.s3boto.S3BotoStorage_AllPublic, as it does not use HTTPS, and
is a good bit faster than S3BotoStorage because it makes some assumptions.

NOTE: This module is primarily aimed at storing and serving images to/from
S3. I have not tested it at all with the standard Django Filesystem backend,
though it *should* work.

## Template Tags

When referring to media in HTML templates you can use custom template tags.
These tags can by accessed by loading the athumb template tag collection.

        {% load thumbnail %}

If you'd like to make the athumb tags global, you can add the following to
your master urls.py file:

    from django.template import add_to_builtins
    add_to_builtins('athumb.templatetags.thumbnail')

Some backends (S3) support https URLs when the requesting page is secure.
In order for the https to be detected, the request must be placed in the
template context with the key 'request'. This can be done automatically by adding
'django.core.context_processors.request' to __TEMPLATE\_CONTEXT\_PROCESSORS__
in settings.py

#### thumbnail

Returns the URL for the specified thumbnail size (as per the object's
models.py Model class):

    {% thumbnail some_obj.image '50x50_cropped' %}

or, to save the value in a template context variable:

    {% thumbnail some_obj.image 'front_page' as 'some_var' %}

As long as you've got Django's request context processor in, the thumbnail tag
will detect when the current view is being served over SSL, and automatically
convert any http to https in the thumbnail URL. If you want to always force
SSL for a thumbnail, add it as an argument like this:

    {% thumbnail some_obj.image '60x60' force_ssl=True %}

To put the thumbnail URL on the context instead of just rendering
it, finish the tag with `as [context_var_name]`:

    {% thumbnail image '60x60' as 'thumb' %}
    <img src="{{thumb}}" />

## To-Do

* See the issue tracker for a list of outstanding things needing doing.

## Change Log

### 2.0

* Complete re-work of the way thumbnails are specified in models.py.
* Removal of the attribute-based image field size retrieval, since we no
  longer are just limited to dimensions.
* Further misc. improvements.

### 1.0

* Initial release.
 
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